This invention relates to fluoropolymer fibers and films which are receptive to cationic modifying agents such as dyes, whiteners, antistatic agents, and flame retardants, and the fibers or films formed by treatment of the receptive fibers or films of the invention therewith. Such fibers and films are useful in various consumer goods where the products are desirably colored, whitened, antistatic or flame retardant.
Among the properties of fluoropolymers, especially perfluorinated polymers, which make them particularly useful are low friction, hydrophobicity, and chemical inertness. These very properties, however, conspire to make dyeing of fluoropolymers problematical since many dyeing processes involve aqueous baths and reactive dye sites. As a result of these problems, it has become common practice to color fluoropolymers using pigments.
In the area of fluoropolymer fibers, pigmentation must be accomplished in the melt prior to fiber spinning. The solid pigment particles have been found in practice to increase the wear on the high precision spinning equipment, while agglomeration of those particles interferes with polymer flow. Furthermore, in use, it is known that pigmented products may undesirably transfer pigmentation to surfaces in contact with them. Still further, pigmented fibers tend to have a dull appearance. Similar considerations apply to the fabrication of films or sheets by melt casting.
It has long been known in the art that polytetrafluoroethylene (PTFE) at molecular weights below ca. 1 million exhibits excessive brittleness for many practical uses. Thus, the most generally useful PTFE resins and products today have molecular weights in excess of 1 million, typically, 10 million, and though exhibiting a melting point, are not for any practical purpose thermoplastic.
It was found many years ago that a tough, lower molecular weight, melt processible copolymer can be made by copolymerizing tetrafluoroethylene (TFE) with various comonomers to form copolymers containing ca. 1-10 mol-% of a branched monomer unit. Among these comonomers are ethylene, hexafluoropropylene (HFP), and perfluoroalkyl vinyl ethers of the formula: CF2=CFxe2x80x94ORf, wherein Rf is a perfluoroalkyl group such as perfluoroethyl, perfluoropropyl, or perfluorobutyl.
It has long been known in the art to add sulfonate functionality to polyester and polyamide fibers to provide a reactive site for cationic dyes. Also known in the art are perfluoroalkoxy sulfonyls of the formula, CF2=CF(Rf)nxe2x80x94OCF2CF2SO2X, wherein Rf is a perfluoroalkyl or a perfluoroalkoxy group, n=0 or 1, and X is F or Cl. Perfluorinated copolymers of TFE and a perfluoroalkoxysulfonyl comonomer of the formula, CF2=CF[xe2x80x94OCF2CF(CF3)]nxe2x80x94OCF2CF2SO2F, wherein n is 0 or 1, and wherein the sulfonyl fluoride group has been hydrolyzed to the related sulfonic acid or sulfonate have long been in widespread commercial use as ion exchange membranes, such as NAFION(copyright) ion exchange membranes, available from DuPont. For many end uses, the sulfonyl moiety is converted into an acid or ionic form which is no longer melt processible but is receptive to cationic dyes. However, the ionic form of the comonomer is known to be highly hygroscopic, the physical properties of the resulting copolymer being highly dependent upon moisture content and exhibiting considerable deterioration at high moisture levels. At comonomer concentrations in the range needed to provide melt processibility, fibers produced from the cation-receptive hydrolyzed form of NAFION(copyright) are excessively moisture sensitive and thus not suitable for many potential applications.
Other copolymers of TFE, such as those derived from the copolymerization of TFE with a monomer containing an alkylvinylether pendant group may exhibit desirable physical properties and no sensitivity to moisture, but are not cation-receptive.
Connolly et al. (U.S. Pat. No. 3,282,875) disclose certain terpolymers of perfluoroalkoxysulfonyl halides, tetrafluoroethylene, and certain perfluoroalkylvinylethers or higher perfluoro olefins, and methods for their synthesis. However, the mole percents used in Connolly for the components of their terpolymers are designed to produce a cross-linked elastomer.
U.S. Pat. No. 3,692,569 (see Example IX) describes a PTFE yarn coated with a copolymer of tetrafluoroethylene and CF2=CFOCF2CF(CF3)OCF2CF2SO2F which is contacted with a solution of NaOH, followed by rinsing and dipping in dilute HCl and rinsing. The resultant yarn was said to be dyeable with xe2x80x9cSevronxe2x80x9d, a cationic dye.
What are needed therefore, are fluoropolymer fibers and films that are receptive to modifying agents such as dyes, whiteners, antistatic agents, and flame retardants, which retain their desirable physical and mechanical properties and which do not have the problems and deficiencies of the prior art.
The present invention provides a blend comprising a first copolymer and a second copolymer; said first copolymer comprising monomeric units of tetrafluoroethylene and a first comonomer selected from the group consisting of: a fluoroalkylvinylether, a fluoroalkene having at least 3 carbons, and ethylene; said second copolymer comprising monomeric units of tetrafluoroethylene and a second comonomer comprising a fluoroalkenyl radical having attached thereto a pendant group comprising a radical represented by the formula:
xe2x80x94(Oxe2x80x94CF2CFR)aOxe2x80x94CF2CFRxe2x80x2Q,
wherein:
R and Rxe2x80x2 are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms;
a=0, 1 or 2;
Q is selected from the group consisting of: xe2x80x94SO3xe2x88x92Z+ and xe2x80x94SO2X;
Z+ is H+, an alkali metal cation, or a cation derived from a compound selected from the group consisting of: a cationic dye, a cationic whitener, a cationic flame retardant, a cationic antistatic agent, and mixtures thereof, and
X is F or Cl;
said first copolymer comprising about 0.5-20 mol-% of the first comonomer; said second copolymer comprising about 5-25 mol-% of the second comonomer; and said blend comprising about 1-10% by weight of said second copolymer. The present invention also provides a fiber or a film comprising such a blend.
The present invention further provides a terpolymer, comprising monomeric units of a first termonomer of tetrafluoroethylene; a second termonomer selected from the group consisting of: a fluoroalkylvinylether, a fluoroalkene having at least 3 carbons, and ethylene; and a third termonomer comprising a fluoroalkenyl radical having attached thereto a pendant group comprising a radical represented by the formula
xe2x80x94(Oxe2x80x94CF2CFR)aOxe2x80x94CF2CFRxe2x80x2Q,
wherein:
R and Rxe2x80x2 are independently selected from F, Cl, or a perfluorinated alkyl group having 1 to 10 carbon atoms;
a=0, 1 or 2;
Q is selected from the group consisting of: xe2x80x94SO3xe2x88x92Z+ and xe2x80x94SO2X;
Z+ is H+, an alkali metal cation, or a cation derived from a compound selected from the group consisting of: a cationic dye, a cationic whitener, a cationic flame retardant, a cationic antistatic agent, and mixtures thereof; and
X is F or Cl;
said terpolymer comprising about 0.5-5 mol-% of the second termonomer and about 0.1-2 mol-% of the third termonomer. The present invention also provides a fiber or a film comprising such a terpolymer.
The present invention further provides a process for producing a shaped article, the process comprising the steps of mixing a first copolymer and a second copolymer to form a mixture, said first copolymer comprising monomeric units of tetrafluoroethylene and a first comonomer selected from the group consisting of a fluoroalkylvinylether, a fluoroalkene having at least 3 carbons, and ethylene; and said second copolymer comprising monomeric units of tetrafluoroethylene and a second comonomer comprising a fluoroalkenyl radical having attached thereto a pendant group comprising a radical represented by the formula xe2x80x94(Oxe2x80x94CF2CFR)aOxe2x80x94CF2CFRxe2x80x2SO2X, wherein R and Rxe2x80x2 are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms; a=0, 1 or 2; and X is F or Cl; said first copolymer comprising about 0.5-20 mol-% of the first comonomer, and said second copolymer comprising about 5-25% of said second comonomer; heating said first and second copolymers simultaneously with or subsequent to mixing, to a temperature sufficient to form a molten blend without significant degradation of either copolymer, said blend comprising about 1-10% by weight of said second copolymer; feeding the molten blend to a shaping device having at least one aperture, each aperture defined therein by a wall; and extruding the molten blend through the at least one aperture to form a shaped article. The present process may further comprise cooling the shaped article and contacting the shaped article with a solution comprising an alkali metal base to yield a cation-receptive shaped article, and may further comprise contacting the cation-receptive shaped article with a cationic modifying agent.
The present invention also provides a process for producing a shaped article, comprising the steps of extruding a composition comprising a molten terpolymer through at least one aperture of a shaping device to form a shaped article, each aperture defined by a wall within said device, said terpolymer comprising monomeric units of a first termonomer of tetrafluoroethylene; a second termonomer selected from the group consisting of a fluoroalkylvinylether, a fluoroalkene having at least 3 carbons, and ethylene; and a third termonomer comprising a fluoroalkenyl radical having attached thereto a pendant group comprising a radical represented by the formula xe2x80x94(Oxe2x80x94CF2CFR)aOxe2x80x94CF2CFRxe2x80x2SO2X, wherein R and Rxe2x80x2 are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms, a=0, 1 or 2, and X is F or Cl; said terpolymer comprising about 0.5-5 mol-% of the second termonomer and about 0.1-2 mol-% of the third termonomer. The process may further comprise cooling the shaped article and contacting the shaped article with a solution comprising an alkali metal base to yield a cation-receptive shaped article, and may further comprise contacting the cation-receptive shaped article with a cationic modifying agent.